Eutrophication is an environmental problem in a majority of shallow water basins all over the world. The flow of nutrients into the water basin leads to an undesired flowering of macroalgae and their decomposition decreases dissolved oxygen which hampers heterothrophic organisms from breathing. Could the macroalgae biomass be harvested and used for biofuels in a sustainable way? Two case studies are analyzed: Orbetello Lagoon, Italy, and Køge bay, Denmark. Today, macroalgae are collected and stored in landfills to limit the problem. This study models a scenario where the macroalgae are used as feedstock for bioethanol. An emergy analysis highlights the most important inputs for the bioethanol production. The growth of algae requires a considerable amount of natural resources in both systems. In particular, water is a fundamental carrier of nutrients in or out of the systems. Consequently, in both systems the collected algae represent the main emergy contribution. However, also the modeled biorefinery is a critical part since it consumes significant amounts of non-renewable resources. In conclusion, at present macroalgae provide environmental problems but in future they may be used as a resource for bioethanol production. Today the management of this biomass is an economically heavy burden for the considered small municipalities. Our analysis has shown that a significant part of the total emergy comes from renewable resources so by overcoming technical barriers inside the biorefinery, e.g. reducing energy consumption, the production may be profitable. This is an encouraging result for third generation biofuels on macroalgal feedstock.
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7th Biennial Conference in Emergy & Environmental Accounting, 2012